A frequent occurrence in drilling a well includes a need to circulate out the mud used during drilling with a different weight mud before production is started. In other procedures, the production string with screens is run into the mud and the mud is displaced with production. The problem here is that the mud can clog the production screens.
Previous efforts employed a swelling material sensitive to well fluids to block a fluid passageway have raised concerns about long term reliability of the material to act as a flow barrier over time. The problem with swelling materials as differential pressure seals is that when they swell they also get very soft and their ability to withstand differential pressures is reduced.
The present invention uses such materials but in a manner where the fact that they get soft is a plus to the operation of the tool into which they are incorporated. In essence, the swelling material that is selected is responsive to produced hydrocarbons to release a latch so that the tool can operate. In an embodiment of a circulation sub, a sliding sleeve with o-ring seals is held open against a closure force by a collet latch. The collets become unsupported when exposed to produced hydrocarbons to close a bypass port previously used to displace drilling mud around the production screens. The softening of the material unlocks the collets from a retaining groove so that an energy source, such as a spring, can push the sleeve to straddle a port with o-rings on a shifting sleeve. These and other aspects of the present invention will be more apparent to those skilled in the art from the description of the preferred embodiment below and the associated drawings, while recognizing that the full scope of the invention is to be found in the claims.